Estimating population sizes can be tricky
- Various techniques based on biology of organism
- enumeration method: capture all animals
- population surveys: deer counts
- Many organisms are not easy to count in a straightforward was
- aquatic organisms
- small animals
- elusive animals
- Often we use indirect methods to calculate population size
Depletion method (DeLury)
- Popular for fish estimates
- Methods relies on:
- CPUE: Catch per unit effort
- Cumulative catch
- The X intercept gives an approximate measure of population size.

Assumptions of DeLury method
- Catchability remains the same
- Intensity of effort stays the same
- methods of capture do not interfere
- Population is constant
- no recruitment or immigration
- no births or deaths
- All organisms are equally vulnerable to capture
- Linear line describes the data!

Mark and Re-capture method

Lincoln-Peterson index


Assumptions of Mark and Re-Capture
- All organisms are equally vulnerable to capture
- Marked individuals are randomly dispersed
- Individuals with marks have the same probability of survival
- Recapture rates are high enough to support an accurate estimate
- Population is constant
- no recruitment or immigration
- no births or deaths

Water Strider Biology
- Predatory insects that skate on the surface of slow-moving water
- To mobile to count easily
- Not overly difficult to catch with nets
- Thorax large enough to mark

Open up the excel file!
